Use the previous context link when checking context extension objects.

src/mips/macro-assembler-mips.cc

Index: src/mips/macro-assembler-mips.cc
diff --git a/src/mips/macro-assembler-mips.cc b/src/mips/macro-assembler-mips.cc
index 4704960039c9256578117a95f963aa7e638ecd19..913bfa5e683e5d4aeecfb2bb623c3b7d94e40002 100644
--- a/src/mips/macro-assembler-mips.cc
+++ b/src/mips/macro-assembler-mips.cc
@@ -3571,12 +3571,9 @@ void MacroAssembler::Abort(const char* msg) {
 void MacroAssembler::LoadContext(Register dst, int context_chain_length) {
   if (context_chain_length > 0) {
     // Move up the chain of contexts to the context containing the slot.
-    lw(dst, MemOperand(cp, Context::SlotOffset(Context::CLOSURE_INDEX)));
-    // Load the function context (which is the incoming, outer context).
-    lw(dst, FieldMemOperand(dst, JSFunction::kContextOffset));
+    lw(dst, MemOperand(cp, Context::SlotOffset(Context::PREVIOUS_INDEX)));
     for (int i = 1; i < context_chain_length; i++) {
-      lw(dst, MemOperand(dst, Context::SlotOffset(Context::CLOSURE_INDEX)));
-      lw(dst, FieldMemOperand(dst, JSFunction::kContextOffset));
+      lw(dst, MemOperand(dst, Context::SlotOffset(Context::PREVIOUS_INDEX)));
     }
   } else {
     // Slot is in the current function context.  Move it into the